1) Field of the Invention
The invention relates to an apparatus and a method for processing video signals, and more particularly, to an apparatus and a method for processing on screen display (OSD) signals and video signals from various sources having different colorimetries.
2) Description of the Related Art
Modern television receivers are designed to receive and process video signals from various sources, for example, analog television signals from a National Television Standards Committee (NTSC) transmission or a video tape, as well as digital video signals transmitted in accordance with the ATSC Digital Television Standard, A/54 (1995). Different signal sources may be encoded according to different colorimetries. “Colorimetry” refers to the combination of color primaries, transfer characteristics, and matrix coefficients associated with generating and processing color representative signals. For example, NTSC signals comply with SMPTE 170M colorimetry and ATSC signals default to comply with ITU-R BT.709 (1990) colorimetry. Additionally, ISO/IEC 13818-2 provides for the broadcaster to specify the input colorimetry to the receiver to allow for other colorimetry combinations.
In view of the possible differences in colorimetries between different signals, it is desirable to design television receiver circuitry with colorimetry compensation so that the video display of the signals from the various sources has a uniform colorimetry. Such circuitry compensates the input video signals such that the color of similar objects are substantially similar regardless of the particular colorimetry. For example, a flesh tone from an ATSC source should appear similar to a flesh tone from an NTSC source.
Television receivers also produce and display OSD graphics that provide information and enable user interface functions. Typically, the OSDs are generated in response to user input to provide information about a program or the receiver, and to allow the user to control functions such as channel selection, image quality and the like. An OSD system usually comprises a common source of OSD signals, which signals are generated by a processing unit in response to received signals or user input, stored in a memory, and then read out and combined with the received video signals. The signals are combined after colorimetry compensation has been performed on the video signal. The OSD signals are combined with the video signals in a mixer that is controlled by a microprocessor. As the lines of the image are traced on a CRT, or a similar display device, the microprocessor selects either the OSD signal or the video signal for output in response to an output of a counter, thereby selectively inserting the OSD image onto the video program image.